The present invention relates to a shadow mask type of color cathode ray tube, and more particularly, to a highly reliable color cathode ray tube in which a shadow mask which serves as a color selecting electrode is improved in formability and shock resistance and is reduced in thermal deformation.
Color cathode ray tubes of the flat face type in which panels (face panels) which constitute image display screens are flattened have rapidly become popular as recent color cathode ray tubes for use as display units in monitor devices for information equipment and color television sets. In the case of a press-molded type of shadow mask (pressed mask) in which an apertured surface is curved in the horizontal and vertical directions, the panel of this flat face type of color cathode ray tube (flat face tube) has an outer surface which is approximately planar, and an inner surface which has a curvature fairly larger than that of the outer surface.
One technical problem encountered in the design of such a flat face tube is the strength of the shadow mask. The shadow mask is molded to have a curvature approximate to that of the inner surface of the panel. Since the inner surface of the panel of the flat face tube has a small curvature compared to a round face tube having curved inner and outer surfaces, the curvature of the shadow mask of the flat face tube must be made small.
For this reason, during press-molding of a plate-shaped member in which color selecting apertures (hereinafter referred to also as electron beam apertures) are formed, a rupture occasionally occurs in a boundary portion between an unapertured region surrounding an apertured region in which the electron beam apertures are formed, and a skirt portion bent from the unapertured region in the direction of the tube axis of the flat face tube, and the rupture leads to defective products. In addition, bridge portions are occasionally cut in the vicinity of the unapertured region.
In addition, a molded shadow mask is occasionally deformed during the process of fixedly securing the shadow mask to a frame, during the process of securing a shadow mask assembly to a panel, or during the transfer of a color cathode ray tube. Furthermore, it is difficult to ensure the strength of the shadow mask against a so-called doming phenomenon such as partial thermal deformation of the apertured region or thermal deformation of the entire shadow mask which occur when the temperature of the shadow mask rises due to collision of electron beams with the shadow mask.
A shadow mask is known in which a step, an inclined surface or a bent portion is formed in a boundary portion between the periphery of the apertured region of its main surface and its skirt portion. This kind of related art is disclosed in, for example, Japanese Utility Model Laid-Open Nos. 40941/1985 and 95334/1992 and Japanese Patent Laid-Open Nos. 349415/1994 and 96726/1996.
As described above, with the recent development of flatter shadow masks (flatter faces), pressures to be applied to shadow masks during press-molding have become larger. Accordingly, it is impossible to directly apply the countermeasures of the above-enumerated related arts to shadow masks for flat faces.
The invention provides a highly reliable color cathode ray tube in which its shadow mask is improved in formability and shock resistance and is reduced in thermal deformation by solving the various problems of the related-art shadow masks.
The gist of the invention for achieving the above object is that a shadow mask incorporated in a color cathode ray tube has a transitional portion made of at least two inclined surfaces in a boundary portion between the outside of an unapertured portion and a skirt portion of the shadow mask.
(1) A color cathode ray tube includes: an evacuated envelope including a panel having an inner surface coated with a fluorescent material for a plurality of colors, a neck in which is housed an electron gun which emits electron beams in a direction of a tube axis of the color cathode ray tube, and a funnel connecting the panel and the neck; and a shadow mask assembly having an apertured region having a multiplicity of color selecting apertures in a main surface disposed in close proximity to and in opposition to the fluorescent material coated on the inner surface of the panel, an unapertured region which surrounds the apertured region, and a skirt portion which is bent in the direction of the tube axis from the unapertured region. In the color cathode ray tube, a transitional portion made of at least two inclined surfaces is provided in a boundary portion between the unapertured region and the skirt portion except the corners of the periphery of the unapertured portion.
(2) In (1), the transitional portion has an outside inclined surface on a side closer to the skirt portion and an inside inclined surface on a side closer to the apertured region, and an angle of the outside inclined surface with respect to the tube axis and an angle of the inside inclined surface in the skirt portion side against the tube axis are both greater than 90xc2x0.
(3) In (1) or (2), an angle formed by the outside inclined surface and the inside inclined surface is in a range of 90xc2x0 less than xcex81xe2x89xa6135xc2x0.
(4) In any of (1) to (3), each of the outer and inside inclined surfaces has an area gradually decreased toward corners of the panel.
(5) In any of (1) to (4), the inside inclined surface has opposite ends located at positions set back from the outside inclined surface at the respective corners.
(6) In any of (1) to (4), the outside inclined surface has opposite ends located at positions set back from the inside inclined surface at the respective corners.
(7) In any of (1) to (6), a curvature of the inside inclined surface, as viewed from the tube axis, is greater than a curvature of the outside inclined surface.
According to each of the above-described constructions, it is possible to prevent a rupture in a shadow mask due to press-working and provide a color cathode ray tube of high reliability which uses a pressed mask resistant to external shock and reduced in thermal deformation.
The number of the inclined surfaces which constitute the transitional portion is not limited to two, and may also be three or four or more as long as press-molding is allowed. In this case, it is desirable that a plurality of inside inclined surfaces be connected to one outside inclined surface. Incidentally, the invention is not limited to any of the above-described constructions nor to any of structures which will be described later in connection with embodiments, and it goes without saying that various modifications can be made without departing from the technical idea of the invention.